The Grey Matter regions of the central
nervous system (CNS), the brain and spinal cord, contrast with the
white matter regions. The grey matter is
the areas where the actual "processing" is done whereas the white matter
provides the communication between different grey matter areas and between
the grey matter and the rest of the body.

The vast majority of multiple sclerosis lesions
occur in the white matter areas but a small number, about 5%, do occur
within the grey matter.

The grey matter is so-called because in section it has
a grey colour due to all the grey nuclei in the cells that make it up.
In fact, in the living body, grey matter is pink.

The neurons in the grey matter
consist of neuronal cell bodies and their dendrites,
the short protrusions that communicate with immediately neighbouring neurons
in the CNS. In contrast with the neurons of the white matter, grey matter
neurons do not contain long axons that transmit
the nerve impulses to more distant regions of the CNS.

About 40% of the human brain is made up of gray matter
whereas 60% is white matter. However the gray matter consumes about 94%
of the total oxygen used by the brain.